The 4 cycle internal combustion engine has four cycles or four strokes that occur in 720° of crankshaft rotation. Each cycle occurs within approximately 180° of crankshaft rotation. The first cycle is the induction cycle or intake stroke in which the intake valve opens as the piston moves over top dead center and starts to move downward or away from the cylinder head. The intake port is connected to the intake manifold which has one end that is exposed to atmospheric pressure. As the piston moves downward it creates a pressure differential or vacuum that allows the atmosphere to fill the cylinder with air. The cylinder fills with air until the intake valve closes. At this point the crankshaft is moving the piston in an upward direction or towards the cylinder head. Both valves, intake and exhaust, are closed as the piston moves upward. As the piston continues its upward movement it compresses and heats the air that has been trapped inside the cylinder. If fuel is added during the induction stroke the fuel will also be heated. As the piston reaches the top of its stroke the heat from the compression will be at its peak. In the spark ignition (SI) internal combustion engine a spark will be generated that will ionize across the spark plug electrodes. This spark will start a chemical reaction between the oxygen and hydrocarbon (gasoline), which will release heat energy that will expand, building pressure in the cylinder. As this pressure builds it will push the piston downward, away from the cylinder head. In the compression ignition (CI) engine fuel will be injected under high pressure into the heated compressed air that is within the cylinder. The heat generated during the compression stroke will start a chemical reaction between the oxygen and hydrocarbons (diesel), which will release heat energy that will build pressure in the cylinder. As this pressure builds it will push the piston downward away from the cylinder head. In either the SI or the CI engines, the chemical reaction propagates across the cylinder head building pressure that will accelerate the piston in a downward movement. Once the reaction between the oxygen and hydrocarbons is completed the exhaust valve will open releasing the remaining pressure into the exhaust manifold. The piston will now move in an upward direction toward the cylinder head forcing the burned gases out of the cylinder into the exhaust manifold. The piston will reach the top of its stroke and the intake valve will once again open and the cycle will start over again. The foregoing is illustrated in FIGS. 1-4 of provisional application Ser. No. 60/842,310, which are incorporated by reference.
Since the conception of the internal combustion engine, combustion efficiency has been a problem. Early on it was a source of power loss. As vehicles have moved into the modern era air quality has become of prime concern. Federal and state government mandates require automobile manufacturers to install equipment to monitor tailpipe emissions. On vehicles newer than 1996, the manufacturer must also install monitors to detect a misfire and turn on the vehicle's malfunction indicator lamp when the emissions levels from the tailpipe exceed 1.5% of the Federal Test Procedure (FTP). A drawback with the FTP requirement is that an intermittent misfire will not produce emission levels exceeding 1.5% of the FTP tailpipe emissions. Therefore a diagnostic trouble code will not be stored in the powertrain control module (the vehicle's onboard microprocessor which monitors and controls the running parameters of the engine) for such a misfiring cylinder or cylinders. Such misfire(s) will, however, cause a drivability problem with the vehicle. It is also known that some vehicles have powertrain control module programming errors that detect and report the incorrect cylinder for the misfire condition. “Misfire” as used herein refers to a range of combustion inefficiencies in a cylinder. Such inefficiencies range from a complete misfire (e.g., where the fuel-air mixture does not ignite at all) to conditions where the efficiency is less than achieved in a normally running engine. Examples of the latter include: lean air/fuel ratio; rich air/fuel ratio; ignition spark weak or out of time; or low compression within the cylinder.
What is needed is a method and apparatus, other than the vehicle's on-board diagnostics, to alert a technician which cylinder (or cylinders) is (are) misfiring. It would also be desirable to find misfiring conditions on older model vehicles and heavy duty vehicles that are compression ignition based. Beyond identifying the cylinder(s) that is (are) misfiring, what is also needed is methodology and apparatus to also identify the probable cause(s) of the misfire(s).
U.S. Pat. No. 7,031,828 to Thompson et al. discloses detecting combustion inefficiencies by monitoring the oxygen level in the vehicle's exhaust path. This patent states that, if the oxygen level peaks, it may be inferred that there was an incomplete explosion in one of the cylinders. The peak in the oxygen level is linked to a particular cylinder in one of two ways. In a first embodiment, a plurality of oxygen sensors is placed in an exhaust manifold. Preferably, each cylinder of the engine has an associated sensor. When a given cylinder vents exhaust that has a high oxygen level, the high oxygen level is detected by the associated sensor and the cylinder is identified as potentially having combustion inefficiency. The sensors may communicate with an onboard computer so that this condition may be monitored and an alarm generated. There is no known engine in current production in which each cylinder has an associated sensor. Further such a system, even if available, could not determine the probable cause or causes of the detected misfires.
The second disclosed embodiment in the Thompson et al. patent addresses testing engines that do not have the sensor system of the first embodiment. As such, this embodiment includes software that, according to Thompson et al., a service technician can use to identify which cylinder in the vehicle is misfiring. This embodiment connects an external probe to a lambda (also known as an O2) sensor already present in the exhaust path of the vehicle. Concurrently, a timing reference is generated that references when the first cylinder of the engine is in the combustion stroke. If there is a peak in the level of oxygen in the exhaust path, a misfire or other combustion inefficiency may be inferred. However, to link the peak in the oxygen level to a particular cylinder, additional information is required in the form of a database of “fingerprints” or “signatures” for the various engine types in service. The length of time between the timing reference point and the peak in the oxygen level is established and compared to the fingerprint or signature for the engine type. From this comparison, it is claimed that the software can determine which cylinder is misfiring.
As is evident from col. 8, l. 38-col. 9, l. 5 and FIG. 8 of the Thompson et al. patent, the method of acquiring a set of fingerprints from a single engine is labor intensive. Given that there are hundreds of automobile engines currently in service in the United States, the impractically of acquiring fingerprints is evident. And, like the first embodiment, there is no way to determine the cause or causes of the detected misfires.
In article entitled Drivability Corner, Motor, June 2006, M. Warren, the use of an exhaust probe and an automotive oscilloscope to locate misfires is disclosed. The exhaust probe is identified as a “First-Look exhaust probe.” The article concludes by stating: “Using an exhaust probe with a scope takes practice, common sense, experience and logical follow-up testing.” The First-Look exhaust “probe” is sensor (specifically a Piezo differential sensor), not a probe (i.e., an electrical probe) as that term is used in the Thompson et al. patent.
Pico Technology is offering for sale the “ACE Missfire Detective” from Thompson Auto Labs. Pico's website (http://www.picotech.com/auto/engine-misfire-detection.html) indicates that the ACE system includes a computer, “ACE Misfire software,” a Pico automotive oscilloscope, and an inductive pick-up. Optionally, if one wants to test through the exhaust, a “FirstLook Sensor,” and a sync probe are required. The website states that: “ACE uses a Pico automotive oscilloscope to identify the high pressure pulse of the exhaust stroke of a misfiring cylinder driven by the unconsumed oxygen of a misfire.” The website also states: “ACE displays a diagram of the engine being worked on and flashes cylinders in firing order sequence.” Healthy cylinders flash green. Cylinders flash red when a misfire is detected. The ACE misfire software is not described. It apparently requires the user to “select the manufacture and type of engine.” There is some sort of data base. “You can add your own vehicles to the data base and updates can also be downloaded from the internet.” The ACE Misfire Detective is also available from Thompson Automotive Labs, LLC and from SenX Technology LLC. The website of SenX, the manufacture of the FirstLook sensor, includes the statement: “ACE software analyzes the exhaust pulse train to identify the lower than normal pulses coming from the exhaust stroke of a misfiring cylinder.” (This appears to be inconsistent with the statement on the Pico website.) U.S. Pat. No. 7,031,828 is also listed. See http://www.senxtech.com/snx_main_ace-misfire-management.html. Both websites indicate that the ACE Misfire Detective is limited to gasoline engines.
The FirstLook sensor is associated by the manufacture with U.S. Pat. No. 6,484,589 to Brock (“Brock I”) and U.S. Patient No. 6,609,416 to Brock (“Brock II”).
As is apparent from the foregoing, the ACE Missfire Detective has the following shortcomings: (1) it is limited to gas engines; (2) there is no live misfire counter (rather the misfires are located in blocks of misfire data); (3) data cannot be streamed continuously; (4) it has problems detecting multiple misfires; and (5) it cannot identify the cause(s) or probable cause(s) of the detected misfires.